System for treating an underground formation

ABSTRACT

A method of treating an underground formation of an oil reservoir, comprising the sequential steps of (a) contacting the formation with an aqueous medium, (b) contacting the underground formation with a hydrocarbon fluid, (c) contacting the underground formation with a solvent in the form of a glycol ether, (d) contacting the underground formation with a first consolidation constituent solution, mainly comprising a poly epoxy resin, (e) contacting the underground formation with second consolidation constituent substantially homogenous solution mainly comprising a curing agent in a solvent.

The present invention relates to a method of treating an undergroundformation. More in particular, the present invention relates to a methodof treating an underground formation in oil and gas reservoirs, by usinga consolidation solution of an epoxy resin and a curing agent. Such amethod was known from e.g. EP 0864032 B1, which actually disclosed amethod of treating an underground formation comprising the sequentialsteps of

-   (a) contacting the formation with an aqueous medium;-   (b) contacting the formation with a hydrocarbon fluid;-   (c) contacting the formation with a solvent in the form of a glycol    ether;-   (d) contacting the formation with a consolidation solution    comprising a monomeric diglycidyl ether of bisphenol A, such as    EPIKOTE 828, in a proportion of from 30 to 60% m and methylene    dianiline as curing agent in a proportion of from 5 to 20% m in the    solvent and-   (e) contacting the formation with a viscosified hydrocarbon fluid    (the so called over-flush) to displace a majority of the resin phase    and to restore the permeability of the treated underground.

As suitable glycol ethers for the solvent were exemplified methoxypropanol, butoxyethanol, hexoxy ethanol and isomers of these glycolethers, which may be optionally mixed with a minor amount (e.g. lessthan 10% m) of a polyethylene glycol, having an average molecular massof around 400, to adjust the viscosity.

It is true that on the other hand was known from ‘Journal of PetroleumTechnology’, December 1966, B. R. Treadway, H. Brandt and P. HaroldParker, page 1537–1543, a three step sand consolidation process. Saidprocess consisted of

-   (1) injecting epoxy resin-   (2) following the displacement of the resin by diesel oil to    establish formation permeability, and-   (3) activating the resin to consolidate the formation by injecting    an activator flush to cure the epoxy resin.

The applied epoxy resin system consisted of pure epoxy resin or an epoxyresin acid anhydride system.

Moreover it was known from ‘52^(nd) Annual Fall Technical Conference andExhibition of the Society of Petroleum Engineers of AIME’, Denver,Colo., Oct. 9–12, 1977, W. L. Penberthy, C. M. Shaugnessy, C. Gruesbeckand W. M. Salathiel (Exxon Production Research Co.), that for effectivesand consolidation, the epoxy resin must wet the surface of the sandgrains and that in those cases where the resins lack this ability apre-flush which preferentially removes water in the presence of oil isessential and particularly when there had been a prior mud acidtreatment. Radial field-scale model studies had demonstrated thatpre-flush effectiveness was dependent on pre-flush volume, viscosity andsand permeability.

Due to the increased economic requirements for present exploitation ofoil reservoirs, in incompetent, high temperature, high pressureformations said underground treating has to be further improved. By theterm incompetent one will understand: formations of insufficientmechanical strength to allow sand-free production.

It will be appreciated that a clear disadvantage of the prior artunderground treating methods was that the actual curing of the suppliedepoxy resin and curing agent did not take place at the desired placesdue to high temperatures in the underground to be treated and/or theinsufficient solubility or dispersability of the applied curing agentsin the glycol ether solvent system or due to an unsuitable viscosity ofthe consolidation solution which caused that the required stoichiometricmutual ratio between epoxy resin molecules and curing agent molecules,could not be reached on the spot or in the specific area to be treated.

It will be appreciated that more in particular, consolidated formationsshould have the strength to withstand stresses induced by adjacent rockstrata and stresses imposed by the flow of fluids into the wellbore.This consolidation strength should be maintained under productionconditions, moreover the consolidated formation should have sufficientpermeability to permit unobstructed flow of fluids into the wellbore andmust show sufficient resistance to the conditions of well stimulationdilute solutions of acids, such as hydrochloric acid, hydrofluoric acidand acetic acid.

An object of the present invention is therefore to provide an improvedmethod of treating hydrocarbon reservoirs in order to eliminate theentrainment of sand minerals and as a consequence wear of productionequipment.

As result of extensive research and experimentation, such improvedtreating method has been surprisingly found.

Accordingly, the invention relates to a method of treating anunderground formation of an oil reservoir in incompetent, hightemperature, high pressure formations, comprising the sequential stepsof

-   a) contacting the formation with an aqueous medium,-   b) contacting the underground formation with a hydrocarbon fluid,-   c) contacting the underground formation with a solvent in the form    of a glycol ether,-   d) contacting the underground formation with a first consolidation    constituent solution, mainly comprising a poly epoxy resin derived    from bisphenols, or a poly phenolic resin (novolac resins), in a    solvent mainly comprising a glycol ether, in an epoxy resin    concentration of from 25 to 75% m and having a viscosity in the    range of from 10 to 100 m Pa.s,-   c) contacting the underground formation with a second constituent    substantially homogenous consolidation solution mainly comprising a    curing agent in a solvent, mainly comprising a hydrocarbon fluid.    Said curing agent occurring in a concentration in the range of from    0.5 to 20% m, and the solution having a viscosity such, that the    ratio between the viscosity of the solution in step (d) and of the    solution in step (e) is in the range of from 1.0 to 5.

With the term ‘mainly comprising’ as used throughout the presentspecification is meant that the specified constituent (i.e. epoxy resinor solvent) is the sole component or can be mixed with minor amounts ofco-components i.e. in amounts of 10% m or less and preferably in amountsof 5% m or less. For example, the preferably applied poly epoxy resin isa poly epoxy novolac resin, which optionally can be mixed with up to 10%m of a diglycidylether of diphenylolpropane (bisphenol A), or ofdiphenylolmethane (bisphenol F).

The applied poly epoxy resin may be derived from phenol, cresols,xylenols, carvacol, cumenol and phenols, substituted with halogen orlower alkyl, having from 1 to 4 C atoms.

More preferably a poly epoxy phenol or cresol novolac resin is used ofthe type which is commercially available as EPIKOTE 154 (Traded byResolution Performance Products).

The aqueous medium used in step (a) can be naturally occurring, treatedi.e. filtered or desalinated water, such as pretreated sea water orwater from rivers, or a KCl or NaCl brine, containing up to 6% m of KClor NaCl, Na₂SO₄, K₂SO₄, NaNO₃, KNO₃ and the like and preferably up to 3%m and more preferably the same brine as originally occurring in theunderground involved.

The hydrocarbon fluid, used in step (b) can be in principle selectedfrom a great variety of hydrocarbons but will be preferably selectedfrom aliphatic hydrocarbons and more preferably gasoils.

The glycol ether solvent to be used in steps (c) and (d) can be selectedfrom ethers of a C₂ to C₆ dihydric alkanol, containing at least one C₁to C₆ alkyl group.

Preferably mono ethers of dihydric alkanols, more preferably glycolethers selected from the group including methoxypropanol, butoxyethanol,hexoxyethanol and the isomers of these glycol ethers, or mixturesthereof.

To adjust the viscosity of said solvent it may further contain a minoramount e.g. less than 10% m, of a polyethylene glycol or polyvinylpyrrolidone, having an average molecular mass of about 400.

The curing agent to be used in the solution of step (e) can be selectedfrom a great variety of usually applied curing agents for epoxy resinswith the restriction that such curing agent must be completely misciblein the applied hydrocarbon fluid in a sufficient degree in order toreach the required concentrations, that the curing agent does notproduce low molecular byproducts during curing and that the finallycured epoxy resin on the spot has sufficient mechanical strength, i.e.between the individual mineral groups on almost only on contact areasand must show a minimal impediment to fluid flow at the curingconditions on the spots to be treated, i.e. high temperature (from 80 to200° C.) and high pressure (from 10 to 100 atm).

Preferably amine type curing agents will be used selected from aliphaticdi or poly amines or alkylaryl amines, more preferably diethylenetoluene diamine, diethylene xylene diamine, diethylene dianiline areused, of which diethylene toluene diamine is the most preferred.

The solvent to be used in the step (e) is a hydrocarbon mixture e.g.SHELLSOL D70, SHELLSOL TD, SHELLSOL D40, SHELLSOL LF (SHELLSOL is aShell Trade mark), EXXSOL D70 EXXSOL 155/170, EXXSOL D220/230 (EXXSOL isa Exxon Mobil Trade mark) HIDRSOL 75/95 N, HYDROSOL 100/130 N (HYDROSOLis a Total Fina Trade mark). To ensure that the viscosity of the mixturein step (e) has a viscosity in excess of that used in step (d), aviscosifier may be used, for example lubricant oil such as VALVATA 460,SHELLVIS 50 (VALVATA & SHELLVIS are Shell Trade mark), Worm Gear Oil(Amoco Oil Co), CYLESSTIC TK-460 (CYLESSTIC is a Exxon Mobil Trade mark)SENATE 460 SENAT is a Gulf Oil Co Trade mark).

It will be appreciated that a catalyst has preferably to be applied forthe efficient curing of the epoxy resin/curing agent on the spot to betreated. Suitable curing catalysts can be selected from salicylic acidand phosphine, phosphonium amine and ammonium catalysts, which aregenerally known in the art.

Said catalyst can be added in amounts of up to 1% m relative to theweight of the total supplied solution either in step (d), i.e. premixedwith the epoxy resin component, or can be added in step, i.e. premixedwith the curing agent in a solvent, of which the latter embodiment ispreferred.

It will be appreciated that such sand consolidation method could meetall the presently desired sand consolidation characteristics, as werespecified herein before.

The invention is further illustrated by the following examples, howeverwithout restricting its scope to these embodiments.

EXAMPLES

To illustrate the effect of method of the present on the unconfinedcompression strength, several samples were made and subjected totreatments. For each test three samples were made of “METTET QUARTZSAND” (96% of the grain diameters are in the range of from 63 to 180 μmand D50=130 μm) in a glass tube, each sample had a diameter of 3.5 cmand a length of 17 cm. After the sand had been placed in the tube theporosity, Φ (in %) was determined. The sand pack was flushed with butaneto remove air, and thereafter the sand pack was flushed with analiphatic hydrocarbon in which butane dissolves to remove the butane.The initial permeability, K_(i) (in Darcy), was determined.

To simulate formation conditions, the following fluids were injected (1)methoxypropanol, (2) brine (2% m KCl); and (3) about 10 pore volumes ofcrude oil to establish irreducible water saturation.

The treatment according to the invention comprises contacting thesamples filled with crude oil at irreducible water saturation in thefollowing sequence: (a) contacting the sample with 2 pore volumes of a2% m KCl brine; (b) contacting the sample with 2 pore volumes of gasoil:(c) contacting the sample with 2 pore volumes of methoxypropanol; (d)contacting the sample with 1 pore volume of a consolidation solution of

Example A

1 pore volume (pv) of 28.8% m:m EPIKOTE 154 in methoxypropanol, followedby 4 pv of 3.7% m:m DETDA in a hydrocarbon solution, consisting of 31.7%m:m SHELLSOL D70 and 68.3% m:m VALVATA460.

Example B

1 pore volume (pv) of 62.0% m:m EPIKOTE 828 in methoxypropanol, followedby 4 pv of 1.96% m:m DETDA in a hydrocarbon solution, consisting of31.7% m:m SHELLSOL D70 and 68.3% m:m VALVATA460.

Example C

1 pore volume (pv) of 38.0% m:m EPIKOTE 154 in methoxypropanol, followedby 4 pv of 7.2% m:m DETDA in a hydrocarbon solution, consisting of 33.1%m:m SHELLSOL D70 and 66.9.3% m:m VALVATA460.

Example D

1 pore volume (pv) of 38.0% m:m EPIKOTE 154 in methoxypropanol, followedby 4 pv of 21.6% m:m DETDA in a hydrocarbon solution, consisting of36.0% m:m SHELLSOL D70 and 64.0% m:m VALVATA460.

Comparative Example

1 pore volume (pv) of 46.5% m:m EPIKOTE 828 and 13.5% MDA m:m inmethoxypropanol, followed by 4 pv of a hydrocarbon solution, consistingof 31.7% m:m SHELLSOL D70 and 68.3% m:m VALVATA460

After the treatment the final permeability, K_(e) (in Darcy), and theunconfined compression strength, UCS (in bar), were determined. Theresults are summarized in Table 1 below.

TABLE 1 Results of the treatment Φ, in % K_(I), in Darcy K_(e), in DarcyUCS, in bar Example A 40 4.54 4.51 180 Example B 40.4 4.34 4.30 106Example C 40.5 4.44 4.15 157 Example D 40.4 4.73 4.28 73 Comparative41.2 4.13 3.96 156

From the examples made according the present invention one canappreciate that the Example treated according to the inventions has ahigher permeability for an excellent to acceptable unconfinedcompression strength compared to the state of the art technology.Moreover it has been found that the drop of permeability for the sampletreated according to the invention is lower than the one reported in theprior art.

1. A method of treating an underground formation of an oil reservoir,comprising the sequential steps of a) contacting the formation with anaqueous medium, b) contacting the underground formation with ahydrocarbon fluid, c) contacting the underground formation with asolvent in the form of a glycol ether, d) contacting the undergroundformation with a first consolidation constituent solution, mainlycomprising a poly epoxy resin derived from bisphenols, or a polyphenolic resin (novolac resins), in a solvent mainly comprising a glycolether, in an epoxy resin concentration of from 25 to 75% (mass) andhaving a viscosity in the range of from 10 to 100 mPa.s, e) contactingthe underground formation with second consolidation constituentsubstantially homogenous solution mainly comprising a curing agent in asolvent mainly comprising a hydrocarbon fluid, said curing agentoccurring in a concentration in the range of from 0.5 to 20% (mass), andthe solution having a viscosity such, that the ratio between theviscosity of the solution in step (d) and of the solution in step (e) isin the range of from 1.0 to
 5. 2. The method of claim 1, wherein theepoxy resin solution is selected from a solid or liquid at 23° C.,epoxy-novolac resin.
 3. The method of claim 2, wherein the epoxy resinsolution is a solid epoxy novalac resin.
 4. The method of claim 1,wherein the curing agent is selected from aliphatic polyamines,alkyl-aryl polyamines and more preferably diethylene toluene diamine(DETDA).